AFTER some confusion over how two Westerners were let aboard, the train pulls out of Phnom Penh at daybreak. The 165-mile journey to Sihanoukville will take 13 hours, at a cost of about 75p.

While we are allowed to stay on the train, two local people are not so privileged. A man with his face covered with a kramah, Cambodia's traditional chequered scarf, and a boy with his T-shirt pulled over his head are ordered to disembark at the next station, a few minutes away. They have leprosy.

"Do you enjoy the train in Cambodia?" inquires the chief of the security unit, sitting on top of a carriage. The last Westerners he asked that question were abducted and later executed by the Khmer Rouge.

Kao Kim recalls the fateful trip on 26 July 1994 which resulted in the deaths of Mark Slater, a Briton, David Wilson of Australia and Jean Michel Braquet, a Frenchman. "I was sitting next to them when we came under fire," he said. "Everybody ducked. Myself, I attacked back with my men. All the passengers were taken hostage, but the soldiers had to run or we would have been killed. I never saw them [the foreigners] again." Recently the BBC cancelled plans for Earl Spencer to take this trip, as part of its Great Railway Journeys of the World series, reckoning it was still too dangerous.

The train doubles its speed to about 12mph as it breaks out of the city and turns southwards. At no point, though, does it travel too quickly to hinder smokers on the roof from lighting up easily. After a while the track parts company with the road and plunges on its own route through the countryside.

Five hours into the journey we pass through the badlands of Phnom Vor, where the train was ambushed. Kao Kim remembers how dangerous his job used to be. "We ran over four mines here once on a single trip," he said. "I cannot count how many times we have been attacked by the Khmer Rouge - too many times. During the civil war, three or four people a month were killed on this line alone."

Although attacks on trains have become less common, particularly since Khmer Rouge forces along the southern line defected to the government in July 1996, Westerners have only recently been allowed back. "Railway stations were not allowed to sell them tickets. Now the railway is safe," claims the security chief, "we can allow foreigners to travel anywhere in the country."

One of his men, Yim Phon, was on the train when it was ambushed in 1994. "We used to have two or three carriages full of soldiers," he recalls. "Now we only take 20. If anyone attacks, we keep shooting until they stop."

Flat cars deployed in front of the locomotive to detonate mines have been removed. "They were not so effective anyway, because they were not heavy enough," says Yim Phon. "Usually the locomotive would set the mines off. We hit at least one every day between 1980 and 1994."

The explosions have taken their toll on the line over the years. A government report recently warned that stretches of the line are "susceptible to sudden collapse", and the carriages pitch violently when they pass over repaired sections. At the many bridges along the way, railway staff stand by to shore up some of the spans before the train passes over. In between these sections, however, progress is stately. The soft purr of the Czech diesel locomotive doesn't drown out the sound of birds and voices.

As the rice ripens, family members come from the cities to help villagers with the harvest. It is a time when young people can see each other away from the watchful eyes of their parents, and the men clown for the attention of the colourfully-clad young women.

"I'll be back tomorrow to help you," shouts Puol Sokhon at some girls from the roof of the train, a line he repeats several times along the way. He has ridden the train nearly every day for the past seven years, loading firewood for about pounds 1 a day.

Like many, he prefers to travel on top to escape the crush of humanity below. "It is better up here," he says. "It is windy, and it doesn't smell. I spend most of my life up here. I take the train down and come back the next day. Sometimes I even sleep up here."

Conductors deftly jump between rooftops collecting fares. "Sometimes the workers fall," says Puol Sokhon. "If they land to the side they generally live, but usually they don't, and they die."

He too recalls the last time he had seen Westerners on the trip. "When the Khmer Rouge attacked, I was faster than anyone else," he said. "I ran into the forest, but they eventually caught me. I never saw the foreigners again." Since the Khmer Rouge in the area defected to the government, former guerrilla fighters have reintegrated into the populace. "I see some of them on the train sometimes, but never the ones who took us hostage and killed the foreigners," he said.

As the track bends up a hill at the base of Bokor mountain past Kampot, the train slows and soldiers eye the treeline with trepidation. "It's not like it used to be," says the security chief. "It feels normal now, but if we see anything unusual, we still shoot until we are through."

Approaching Sihanoukville after nightfall, soldiers on the locomotive shine torches into the forest. At one point they see movement and fire a warning shot, but nothing more comes of it. Other soldiers hardly look up. They have seen worse.